文摘
Land use and agricultural practices modify both the amounts and properties of C and N in soil organic matter. In order to evaluate land use and management-dependent modifications of stable and labile C and N soil pools, (i) organic C and total N content, (ii) microbial (Cmic) and N (Nmic) content and (iii) C and N mineralisation rates, termed biologically active C and N, were estimated in arable, grassland and forest soils from northern and southern Germany. The C/N-ratios were calculated for the three levels (i)–(iii) and linked to the eco-physiological quotients of biotic-fixed C and N (Cmic/Corg, Nmic/Nt) and biomass-specific C and N mineralisation rate (qCO2, qNmin). Correlations could mainly be determined between organic C, total N, Cmic, Nmic and C mineralisation for the broader data set of the land use systems. Generally, the mineralisation activity rate at 22 °C was highly variable and ranged between 0.11 and 17.67 μg CO2–C g−1 soil h−1 and −0.12 and 3.81 μg (δNH4++δNO3−)–N g−1 soil h−1. Negative N data may be derived from both N immobilisation and N volatilisation during the experiments. The ratio between C and N mineralisation rate differed significantly between the soils ranging from 5 to 37, and was not correlated to the soil C/N ratio and Cmic/Nmic ratio. The C/N ratio in the biologically active pool was significantly smaller in soils under conventional farming than those under organic farming systems. In a beech forest, it increased from the L, Of to the Ah horizon. The biologically active C and N pools refer to the current microbial eco-physiology and are related to the need for being C and N use efficient as indicated by metabolic qCO2 and qNmin quotients.